1. Field of the Invention
The present invention relates to a riding lawn mower having a mower unit attached to a lower part of a chassis frame, and a driver's seat mounted on an upper part of the chassis frame.
2. Description of the Related Art
In this type of riding lawn mower, as disclosed in U.S. Pat. No. 5,207,187, for example, the chassis frame is supported by front wheels and rear wheels through a transmission case and an axle case. Rear wheel fenders are attached to the chassis frame, and a driver's seat is mounted on the fenders. The driver's seat has one end thereof supported by the fenders to be pivotable about a transverse axis, with the other end of the seat connected to the fenders through a suspension mechanism in the form of springs. This construction allows a limited distance between the transverse axis and suspension mechanism. Consequently, the suspension mechanism alone cannot fully absorb vibrations caused by uneven ground surfaces and transmitted from the wheels. This construction provides little comfort to the seated driver.
In order that the driver's seat may give improved comfort, it is conceivable to connect the rear wheels to the chassis frame indirectly through a suspension mechanism. That is, a frame supported by the rear wheels is connected to a rear portion of the chassis frame to be vertically pivotable about a transverse axis, and a suspension mechanism is mounted between the rear wheel frame and chassis frame. Alternatively, as disclosed in Japanese Patent Publication Kokai No. 2-208132, the chassis frame may be connected to the rear wheels through a suspension mechanism. A grass cutting operation is carried out often with a gauge wheel of the mower unit raised from the ground, as otherwise the gauge wheel could harm the grass. However, in either of the above support structures where the chassis frame is connected to the rear wheels through a suspension mechanism, the suspension mechanism in its cushioning motion causes the chassis frame to move vertically toward and away from the ground during such a grass cutting operation. As a result, variations occur in height over the ground of the mower unit attached to the chassis frame. This brings about a drawback of uneven cutting height which is intolerable from the standpoint of mower's performance.